Fifth grade Olympiad questions, urgent~~Limit to give me the answer in two minutes after you see it (you have to write the process)

South Town to North Town is a longer way up the hill than North Town to South Town (the red line in the diagram)

Because the two black lines on the way are equal in distance so the time to go up and down the hill is equal.

For every kilometer traveled, it takes 1/2-1/5=3/10 (hours) more time to go uphill than downhill

The red part of the line is longer (38-32)÷(3/10)=20 (kilometers) This part of the way up the hill takes 20 ÷ 2=10 (hours)

On the two black lines, one goes uphill and the other one goes downhill **** It takes 38-10=28 (hours)

one kilometer uphill + one kilometer downhill *** takes time 1/2 + 1/5 = 7/10 (hours)

The black line is 28 ÷ (7/10) = 40 (kilometers)

South to north (one red line and two black lines) 40 × 2 + 20 = 100 (kilometers)